Messungen der Bildfehler eines elektrostatischen Sektorfeldes / Measurement of Image Aberrations of an Electrostatic Sector Field

The ion-optical properties of a cylinder-condenser (sector angle φ = 50° and curvature radius of the middle equipotential surface r = 100mm) are investigated by an experimental ray-tracing technique. A narrow electron beam entering the field under a known angle and at a known place is observed on the exit side of the field by means of a luminescent screen combined with a special micro-scope. The measurement of the lateral distances of this ray from the central beam in several distances behind the exit field-boundary yields the information about the imaging properties of the sector field. The analysis of the measurements indicates the existence of a third-order angular aberration. The experimentally determined values of second-order α-, u-, and δ-aberration-coefficients do not differ substantially from the theoretical ones.